diff --git a/convert.c b/convert.c
index 0d6fb3410a..df7186bd81 100644
--- a/convert.c
+++ b/convert.c
@@ -613,7 +613,7 @@ static int crlf_to_worktree(const char *src, size_t len, struct strbuf *buf,
 
 struct filter_params {
 	const char *src;
-	unsigned long size;
+	size_t size;
 	int fd;
 	const char *cmd;
 	const char *path;
diff --git a/t/t1051-large-conversion.sh b/t/t1051-large-conversion.sh
index 8b23d86260..d4cfe8bf5d 100755
--- a/t/t1051-large-conversion.sh
+++ b/t/t1051-large-conversion.sh
@@ -97,4 +97,15 @@ test_expect_success EXPENSIVE,SIZE_T_IS_64BIT,!LONG_IS_64BIT \
 	test "$size" -ge $((5 * 1024 * 1024 * 1024))
 '
 
+# This clean filter writes down the size of input it receives. By checking against
+# the actual size, we ensure that cleaning doesn't mangle large files on 64-bit Windows.
+test_expect_success EXPENSIVE,SIZE_T_IS_64BIT,!LONG_IS_64BIT \
+		'files over 4GB convert on input' '
+	test-tool genzeros $((5*1024*1024*1024)) >big &&
+	test_config filter.checklarge.clean "wc -c >big.size" &&
+	echo "big filter=checklarge" >.gitattributes &&
+	git add big &&
+	test $(test_file_size big) -eq $(cat big.size)
+'
+
 test_done